Fish Oil May Cause Difference in Rate of Depression between Genders

Eating fish, especially those containing one polyunsaturated fatty acid, appears to be associated with a lower prevalence of depressive symptoms in adolescent boys — but not in girls — Japanese researchers reported.

In a study of more than 6,500 Japanese teenagers, the highest intake of eicosapentaenoic acid (EPA) — one of two omega-3 fatty acids found in certain fish — was associated with reduced odds of depressive symptoms in boys (P for trend=0.04) according to Kentaro Murakami, PhD, of the University of Tokyo, and colleagues.

But for reasons that remain unclear, the same links weren’t seen among girls in the cross-sectional study of junior high students in two cities on the island of Okinawa, the researchers reported online in the journal Pediatrics.

These findings add to the varied and often contradictory evidence about the relationship of depression with consumption of fish and the two long-chain omega-3 polyunsaturated fats — EPA and docosahexaenoic acid (DHA) — contained in fish such as mackerel and salmon, Murakami and colleagues noted.

Studies have suggested that omega-3 fats may play an important role in neurotransmitter activity related to depression, according to background provided by the authors.

Fish consumption is high in Japan and few studies of fish and omega-3 consumption have been conducted in non-Western populations, they noted.

All of the previous studies were conducted among adults and none in a younger population, the researchers added.

So Murakami and colleagues turned to the Ryukyus Child Health Study, which took place in two cities on the island province of Okinawa, to study various health factors among children. The team used two self-administered questionnaires distributed to all eligible junior high school students — a total of 12,451 youths ages 12 through 15.

One was a food-frequency questionnaire that included selected foods commonly eaten in Japan and dietary behavior. Types of fish listed in the questionnaire included those especially high in EPA and DHA, such as canned tuna, sardines, mackerel, salmon, and trout, as well as yellow tail, Pacific herring, eel, whitefish, and freshwater fish.

The other questionnaire was a Japanese version of the Center for Epidemiologic Studies Depression (CES-D) scale, which consists of 20 questions that address six symptoms of depression experienced during the preceding week.

Complete data was available for 6,517 students — including 3,067 boys and 3,450 girls.

Murakami and colleagues looked for associations between depressive symptoms and fish consumption and intake of either EPA or DHA or both together.

The presence of depressive symptoms was defined as a score of at least 16 on the 60-point CES-D scale, the researchers said. By that measure, the prevalence of depressive symptoms was 22.5 percent among the boys and 31.2 percent for girls.

For the boys, after adjusting for potential confounding factors, they also found:

Fish intake was inversely associated with the risk of depressive symptoms. The adjusted odds ratio was 0.73 when the highest quintile of intake was compared with the lowest; the significance level of the trend was P=0 .04 (95 percent CI, 0.55 to 0.97).

EPA intake also showed an independent and inverse association with depressive symptoms and the adjusted odds ratio was similar at 0.71 (P for trend=0.04, 95 percent CI, 0.54 to 0.94).

Intake of DHA showed a similar inverse association, but the trend did not reach significance.

Consuming both EPA and DHA was also inversely associated with the risk of depressive symptoms — and the odds ratio was similar — but again the trend did not reach significance.

In girls the odds ratios all hovered around 1.0, with no significant trends from lowest to highest quintile of consumption, Murakami and colleagues found.

But the reasons for this lack of an association were not clear, they wrote.

One possibility is that the genetic component of depression is stronger in females than in males, so diet may play a lesser role in girls. There is also evidence, the researchers noted, that females store the fatty acids more effectively, meaning even girls whose intake was low might have sufficient reserves.

Limitations of the study included its cross-sectional design, which cannot establish causality, the researchers noted.

Food-frequency was self-reported. The presence of depressive symptoms was determined by questionnaire, rather than a structured diagnostic interview, and data were collected from around half of eligible participants, the authors noted.

And, despite adjustment, residual confounding by other factors could have biased the results, they wrote.

As well, environmental factors in Okinawa may be sufficiently different from other places that the results will not apply elsewhere, Murakami and colleagues wrote.

Since the study was conducted among Japanese youth, the results may not be generalizable.

The researchers stressed that their findings require confirmation by additional prospective studies and also by trials with a more rigorous assessment of dietary intake and depressive symptoms.